The present invention relates to nano-scale patterning techniques. More specifically, the present invention relates to methods for directly converting a non-magnetic single layer or multi layer film into a patterned magnetic nanostructure by mask-controlled local phase transition.
Conventionally, a magnetic recording medium for a hard disk is produced by sputter depositing a Co-alloy thin film on a chromium-based underlayer, as disclosed for example in U.S. Pat. No. 5,693,426. The term xe2x80x9cunderlayerxe2x80x9d refers to a layer of thin film, which is deposited below the magnetic layer of a recording medium. The purpose of an underlayer is to provide favorable crystalline growth conditions for the magnetic layer and to achieve many useful recording properties. In the current magnetic recording materials, the underlayers are made of NiAI layer and a Cr layer.
The magnetization vectors written on such disks lie in the plane of the film and are not stable enough at higher densities. Therefore, the current media are not expected to support densities higher than 300 Gb/in2 (see, for example, DATA STORAGE, p. 41-48, Sepetember 1998). Different alternatives such as perpendicular magnetic recording (in which the magnetization vectors of the written bits lie perpendicular to the film and are more stable), or patterned structures of elements (patterned media) are sought for high-density recording media.
Problems with writing on perpendicular medium prevent perpendicular recording from taking off despite its promise of higher densities with respect to longitudinal recording (see, for example, J. MAGN. MAGN. MATER., vol. 209, p. 1-5, 2000). The patterned structures of magnetic nanoelements offer thermal stability, good signal/noise at high densities (media noise determined primarily by lithography) and a huge advantage for tracking, both through built-in patterns and one-pass servowriting.
So far, techniques such as electron or ion beam lithography (see, for example, J. VAC. SCI. TECHNOL. B 12, pa. 3695, 1994), laser interferometry (see, for example, IEEE. TRANS. MAGN. 32, P. 4472, 1996), and nanoimprint lithography (NIL) (see, for example, U.S. Pat. No. 5,772,905) have been employed for producing patterned nanostructures. Patterned nanostructures have also been fabricated using an atomic force microscope or a scanning tunneling microscope (see, for example, J. APPL. PHYS., Vol. 76, P. 6656, 1994). Unfortunately, however, these methods have not been suitable for mass production. With electron (ion) beam lithography, a number of processing steps are typically involved, the production rate is slow, and the cost is high. NIL also involves many processing steps. As such, it is generally believed that there are no viable technologies for fabricating patterned nanostructures, and more particularly patterned arrays, with the dimensions required for the individual elements over an area large enough to contribute to useful memory and with low cost.
In view of the foregoing, it is the aim of the present invention to provide an alternative method of fabricating patterned nanostructures.
The invention relates, in one embodiment, to a method of converting a potentially magnetic material into a magnetic patterned nanostructure by using mask-controlled local phase transition. The term xe2x80x9cpotentially magneticxe2x80x9d generally refers to a non-magnetic state that can be converted into a magnetic state, i.e., the non-magnetic state has the xe2x80x9cpotentialxe2x80x9d to turn into a magnetic state. In most cases, the phase transition is implemented by local annealing and/or mixing of a non-magnetic or weak-magnetic film having a single or multiple layer.
The invention relates, in another embodiment, to a method of producing a patterned magnetic nanostructure. The method includes providing a substrate having a non-magnetic single layer or multi layer film that can be converted into a magnetic state by annealing and/or mixing. The method further includes covering the substrate with a mask having a desired pattern and resolution associated with the patterned magnetic nanostructure. The method also includes transferring the desired pattern from the mask to the film by converting desired portions of the non-magnetic film to a magnetic state via annealing and/or mixing.
The invention relates, in another embodiment, to a method of producing a patterned magnetic nanostructure. The method includes providing a substrate having a single layer or multi layer film that can be converted into a magnetic state by annealing and/or mixing. The method further includes positioning a mask on or over the film. The mask has a desired pattern and resolution associated with the patterned magnetic nanostructure. The method additionally includes subjecting the mask-covered substrate to a beam of radiation having sufficient energy to locally anneal and/or mix the non-magnetic or weak-magnetic single-layer or multi layer film. Because of the mask, only desired portions of the non-magnetic film are exposed to the beam of radiation to produce an array of magnetic elements in a non-magnetic matrix.